1. Technical Field
The present invention relates to optical scanners and image forming apparatuses.
2. Related Art
One known example of an optical scanner for drawing by optical scanning in a laser printer or the like is formed of a torsion oscillator and uses an actuator (see, for example, JP-A-2005-181395).
In JP-A-2005-181395, an actuator has an insulated substrate in which a pair of permanent magnets is provided. Further, a scanner main body is supported by the insulated substrate between the pair of permanent magnets. The scanner main body has a frame-shaped supporting section, a frame-shaped outside movable plate inside the supporting section, and an inside movable plate (mirror) inside the outside movable plate. The outside movable plate is connected to a supporting section via a pair of first torsion bars extending in an X-axis direction, and the inside movable plate is connected to the outside movable plate via a second torsion bar extending in a Y-axis direction perpendicular to the X-axis direction. Finally, the outside movable plate and the inside movable plate each have a coil.
In the actuator structured as described above, by the action of the magnetic fields produced from the coils and the magnetic field produced between the pair of permanent magnets by energization, the outside movable plate turns about the X axis with the inside movable plate by using the first torsion bar as a central axis, and the inside movable plate turns about the Y axis by using the second torsion bar as a central axis.
As described above, in the actuator of JP-A-2005-181395, the mechanism which turns the inside movable plate about the X axis and the mechanism which turns the inside movable plate about the Y axis differ from each other. This makes it impossible to turn the inside movable plate about the X axis and the Y axis under the same conditions. In addition, in the actuator of JP-A-2005-181395, the magnetic field produced from the coil in the outside movable plate and the magnetic field produced from the coil in the inside movable plate interfere with each other, making it impossible to turn the inside movable plate about the X axis and the Y axis independently. Thus, in the actuator of JP-A-2005-181395, it is impossible to turn the inside movable plate about the X axis and the Y axis with stability.